1. Field of the Invention
The present invention relates to a tracking type laser gauge interferometer.
2. Description of the Related Art
Conventionally, a tracking type laser gauge interferometer is known which is comprised of a first recursive reflector provided at a predetermined position to reflect light parallel to incident light; a second recursive reflector attached to a measurement object; a main body part for guiding to the first recursive reflector light emitted from a laser light source and making emergent the light reflected at the first recursive reflector; a rotating mechanism for rotating the main body part about the first recursive reflector; and a control unit for controlling the rotating mechanism on the basis of the light emergent from the main body part and reflected at the second recursive reflector, so as to measure the distance between the recursive reflectors while tracking the second recursive reflector (e.g., refer to JP-A-7-120213).
The tracking type laser interferometer (tracking type laser gauge interferometer) described in JP-A-7-120213 has two cat's eyes (first recursive reflector and second recursive reflector), a rotating part (main body part), a supporting frame serving as the rotating mechanism, two motors, and the control unit, and measures the distance between the cat's eyes while tracking the cat's eye serving as the second recursive reflector. In addition, with the tracking type laser interferometer described in JP-A-7-120213, in the state in which the rotating mechanism is not rotating about the cat's eye serving as the first recursive reflector, the rotating portion is rotated by using as axes two axes which are perpendicular to the traveling direction of the light incident on this cat's eye. Accordingly, the tracking type laser interferometer described in JP-A-7-120213 is capable of calculating the position of a moving body on the basis of the rotational angle of the rotating mechanism and the distance between the cat's eyes.
However, since motion errors occur in the rotating mechanism, the tracking type laser interferometer described in JP-A-7-120213 has a problem in that it is unable to properly acquire the rotational angle of the rotating mechanism, and is hence unable to properly calculate the position of the moving object.